Hook-On Scaffold

ABSTRACT

A scaffold assembly comprising at least one pair of hook-on scaffold elements; said scaffold elements adapted for support of at least one builder&#39;s plank; each of said elements comprising a vertical main shaft provided with a hook structure at an upper end of said main shaft and a securing bracket at a lower end of said main shaft; each of said hook-on scaffold elements further comprising a braced hook-on arm; said hook structure adapted for engagement with a horizontal top plate of a building frame, and said securing bracket adapted for engagement with a vertical stud or a horizontal element of said building frame.

The present invention relates to safety devices for use in theconstruction of buildings and, more particularly to support structuresfor personnel working above ground level.

BACKGROUND

Safety of personnel involved in the building industry has increasinglybecome the subject of regulation. A particularly dangerous aspect ofwork on construction sites is where personnel is required to work atsome height above ground level, for example on two-story buildings orwhere steeply sloping terrain is involved.

In at least some jurisdictions it is now a requirement that scaffoldingbe installed where personnel is required to work at a greater than a setheight above ground level. Scaffolding supported at ground levelinvolves the erection of a large number of structural elements of frameswith adjustable feet, cross bracing and fasteners etc, being expensivein both material and labour. Moreover, where sloping ground, projectingpatios and other obstructions are encountered, the use of scaffoldingbecomes particularly awkward and time consuming.

It is an object of the present invention to address or ameliorate someof the above disadvantages.

Note:

The term “comprising” (and grammatical variations thereof) is used inthis specification in the inclusive sense of “having” or “including”,and not in the exclusive sense of “consisting only of”.

BRIEF DESCRIPTION OF INVENTION

Accordingly, in a first broad form of the invention, there is provided ascaffold assembly comprising at least one pair of hook-on scaffoldelements; said scaffold elements adapted for support of at least onebuilder's plank; each of said elements comprising a vertical main shaftprovided with a hook structure at an upper end of said main shaft and asecuring bracket at a lower end of said main shaft; each of said hook-onscaffold elements further comprising a braced hook-on arm; said hookstructure adapted for engagement with a horizontal top plate of abuilding frame, and said securing bracket adapted for engagement with avertical stud or a horizontal element of said building frame.

Preferably, said assembly further comprises a safety rail assembly forattachment to said pair of hook-on scaffold elements.

Preferably, said vertical main shaft comprises a length of metalrectangular hollow section; said main shaft provided at intervals alongits length with hooking eyes projecting from said main shaft in a firstoutward direction; said hooking eyes adapted for engagement with saidbraced hook-on arm.

Preferably, said hook structure comprises a metal horizontal plateprojecting from said upper end of said main shaft in a second inwarddirection; said hook structure further including a metal vertical platedepending from an outer end of said horizontal plate.

Preferably, said metal horizontal plate is provided with a strengtheningrib extending substantially the length of said plate.

Preferably, said securing bracket comprises a generally U-shapedfabrication comprising a spaced apart pair of arms extending from a backplate in said second inward direction; said arms adapted to acceptbetween them a said vertical stud or a horizontal element of said frame.

Preferably, said pair of arms are of a length so as to project past aninner face of said vertical stud or horizontal element; outer ends ofsaid arms provided with apertures adapted to accept therethrough asecuring element so as to secure said securing bracket to said verticalstud or said horizontal element.

Preferably, said securing element is a first wing bolt passing through afirst of said apertures in a first of said arms and threadably engagingwith a threaded one of said apertures in a second of said arms.

Preferably, one of said arms is provided with a threaded aperture at amedian position along said arm; said threaded aperture adapted to accepta second wing bolt; said second wing bolt adapted for engagement withsaid vertical stud or said horizontal member so as to prevent anymovement of said bracket relative said vertical stud or said horizontalelement.

Preferably, each said first wing bolt and said second wing bolt aresecured to said bracket by a length of chain.

Preferably, said securing bracket is rotatably attached to said mainshaft; attachment of said securing bracket arranged so as to allow saidbracket to rotate 90 degrees between a first position for engagementwith said vertical stud and a second position for engagement with saidhorizontal element.

Preferably, said hooking eyes comprise U-shaped elements projectinghorizontally from said main shaft; arms of said U-shaped elementsattached to opposing sides of said main shaft, and wherein separationbetween an outer face of said main shaft and inside faces of cross barsof said U-shaped elements is adapted to accept hooking lugs of saidbraced hook-on arm.

Preferably, said main shaft is provided with at least one pair of saidhooking eyes.

Preferably, said main shaft is provided with two pairs of said hookingeyes; said two pairs providing two levels of attachment of said hook-onarm.

Preferably, one of each of said at least one pair of hooking eyes isprovided with an aperture through said cross bar of said U-shapedelement; said aperture adapted to receive a spring-loaded pin forsecuring one of said hooking lugs inserted in said hooking eye.

Preferably, said braced hook-on arm comprises a horizontal supportmember, an angled bracing member and at least one intermediate bracemember extending between said horizontal supporting member and saidangled bracing member.

Preferably, an inner end of each of said horizontal support member andsaid angled bracing member is provided with one of said hooking lugs;each respective one of said hooking lugs adapted for insertion into acorresponding one of said pair of hooking eyes.

Preferably, one of said hooking lugs for said horizontal support memberis provided with an aperture adapted for passage therethrough of saidspring-loaded pin; said spring-loaded pin passing through said aperturein a said hooking eye when said braced hook-on arm is assembled to saidmain shaft.

Preferably, said horizontal support member is of length sufficient tosupport thereon two side-by-side said builder's planks.

Preferably, an inner end and an outer end of said horizontal supportmember are provided with retaining plank safety hook elements; saidsafety hook elements adapted to retain respective outer edges of saidside-by-side builder's planks.

Preferably, said horizontal support member is further provided at anouter end with a vertical safety rail support element.

Preferably, adjoining ones of said hook-on scaffold elements in use areadapted to each support a stanchion of said safety railing in arespective said safety rail support element; said safety railingextending between said adjoining hook-on scaffold elements; said safetyrail comprising a pair of said stanchions and upper and lower horizontalrail elements.

Preferably, said stanchions and said horizontal rail elements areinterconnected by snap-lock hooks.

Preferably, said horizontal rail elements comprise telescoping inner andouter tube members; said inner and outer tube members allowingadjustment of length of said safety railing between adjoining saidstanchions.

Preferably, said upper end of said vertical main shaft is provided withat least one bracket for attachment of a cross bracing member of saidsafety railing.

Preferably, said cross bracing member comprises a tubular memberprovided at a first inner end with a locking structure adapted forengagement with said at least one bracket; said tubular member providedat a second outer end with a snap-lock hook for engagement with saidupper rail element of said safety railing.

Preferably, said locking structure comprises a spring-loaded pinassembly; said spring-loaded pin engaging with an aperture provided insaid at least one bracket so as to secure said cross bracing member frominadvertent disengagement with said at least one bracket.

In a further broad form of the invention, there is provided a builder'splank support system adapted for attachment to frame elements of abuilding; said system including a scaffold assembly provided with a hookplate at an upper end of said scaffold assembly and a securing bracketat a lower end; said securing bracket adapted for fastening to avertical stud or a horizontal element of said frame.

In yet a further broad form of the invention, there is provided a methodfor supporting at least one builder's plank and safety railing at theside of a building; said method including the steps of:

-   -   (a) hooking a hook plate of at least one pair of hook-on        scaffold assemblies over a horizontal top plate of a frame of        said building,    -   (b) securing a bracket of each of said scaffold assemblies to a        vertical stud or a horizontal element of said frame,    -   (c) positioning said at least one builder's plank over        horizontal members of hook-on arms of said at least one pair of        said scaffold assemblies.

Preferably, said method further includes the steps of;

-   -   (a) inserting stanchions of said safety railing into stanchion        support elements of said scaffold assemblies,    -   (b) attaching horizontal railing elements to said stanchions,    -   (c) bracing said railings by cross bracing members extending        between said railings and brackets on vertical shafts of said at        least one pair of scaffold assemblies.

In still a further broad form of the invention, there is provided asafety system for personnel engaged in construction of a building; saidsystem including a scaffold assembly adapted for attachment to elementsof a frame of said building; adjoining ones of said scaffold assemblyadapted for support of at least one builder's plank and a safetyrailing, and wherein a lower end of said scaffold assembly is secured bya bracket to a vertical stud or a horizontal element of said frame.

BRIEF DESCRIPTION OF DRAWINGS

Embodiments of the present invention will now be described withreference to the accompanying drawings wherein:

FIG. 1 is a side elevation view of a hook-on scaffold assembly accordingto a preferred embodiment of the invention,

FIG. 2 is a perspective view of a main vertical shaft and associatedcomponents of the scaffold assembly of FIG. 1,

FIG. 2A is a perspective view of the upper end of the main verticalshaft of FIG. 2,

FIG. 3 is a perspective view of a hook-on arm of the scaffold assemblyof FIG. 1,

FIG. 3A is an enlarged side view of a spring-loaded pin mechanism of thehook-on arm of FIG. 3,

FIG. 4 is a perspective detailed view of a securing bracket of thescaffold assembly of FIGS. 1 and 2,

FIG. 5 are representations of bolts for use with the scaffold assemblyof FIGS. 1 to 4,

FIG. 6 is a perspective view of a safety railing for attachment to thescaffold assembly of FIG. 1,

FIG. 7 is a detail view of the inner end of a cross bracing member ofthe safety railing attachment of FIG. 6,

FIG. 8 is a perspective view of a pair of scaffold assemblies of FIG. 1attached to the frame of a building and supporting a pair of builder'splanks and a safety railing.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

With reference to FIG. 1, a scaffold assembly 10 according to apreferred embodiment of the invention, comprises a vertical main shaft12 and a braced hook-on arm 14. Main shaft 12 includes a vertical lengthof rectangular section tubing 16 to which is affixed at an upper end 18a hook structure 20. Hook structure 20 may be formed of a piece of steelangle, strengthened with a rib 21 as shown in FIG. 2A.

A securing bracket 22 is rotatably attached at a lower end 24 of tubing16. Also attached at intervals along the lower portion of the length oftubing 16, are two pairs of first hooking eyes 23 and 23A, and 26 and26A in the form of U-shaped brackets as best seen in FIG. 2. Attached atupper end 18 of main shaft 12 are a further pair of hooking eyes 25 and25A, shown in more detail in FIG. 2A.

Braced hook-on arm 14 comprises a horizontal support member 28, and anangled bracing member 30 formed of flat bars (or rectangular sectiontubing) affixed one to the other towards their respective outer ends andprovided with intermediate bracing elements 32. Both the inner end ofhorizontal support member 28 and angled bracing member 30 are providedwith vertical hooking lugs 34 and 36 respectively (as best seen in FIG.3), adapted for insertion into either the upper pair 23 and 23A, or thelower pair of hooking eyes 26 and 26A.

Sides of the U-shaped pairs of brackets 23 and 23A, and 26 and 26A, areaffixed to opposite sides of tubing 16 such that a sufficient gap isleft between the inside faces of the base of the brackets and theoutside face of tubing 16 for insertion of vertical hooking lugs 34 and36. The upper brackets 25 and 25A are similarly constructed andarranged; in this case to accept a cross brace 110 of the safety railingsystem to be further described below.

Braced hook-on arm 14 is provided with a spring loaded pin mechanism 33(shown in enlarged detail in FIG. 3A) located on the underside and atthe inner end of horizontal support member 28. Mechanism 33 comprises aU-shaped bracket 41 with apertures in the legs of the bracket forslidingly retaining pin 38. Pin 38 is provided with a washer 39, weldedto pin 38, and a coaxial compression spring 43 retained between washer39 and the inside of bracket 41. Pin 38 is further provided with anaperture 47 at an outer end of pin 38 for attachment of a split ring 45,by which means pin 38 may be pulled into a retracted position relativeto vertical hooking lug 34. Vertical hooking lug 34 is provided with ahole 37 (as shown in FIG. 3) coaxial with pin 38 of mechanism 33.

Each of the upper ones 23 or 26 of the pairs of brackets 23 and 23A, and26 and 26A, is provided with a hole 27, the arrangement being such thatwhen lug 36 is inserted into a bracket 23 or 26, initially with pin 38of spring-loaded mechanism 33 retracted, the pin 38 is driven by spring43 through holes 37 and 27 in vertical hooking lug 34 and bracket 23 or26 respectively (as best seen in FIG. 1) to secure braced hook-on arm 14to main shaft 12. Main shaft 12 may also be provided with apertures 29axially aligned with apertures 27 of brackets 23 and 26 such that with asufficiently long pin 38, the end of the pin passes through the wall oftubing 16.

The vertical hooking lug 34 of horizontal support member 28 is extendedupwards to incorporate an inner end safety hook element 40. An outer endsafety hook element 42 is provided near the outer end of horizontalsupport member 28. Half way between these safety hook elements 40 and 42is a divider lug 46. The length of horizontal support member 28 and thedistances between the divider lug 46 and insides of safety hook elements40 and 42 is such as to provide support for two side by side standardbuilder's planks 44.

The outermost end of horizontal support member 28 is provided with avertical safety rail support element 48, which is adapted to receive anupright 102 of a safety rail assembly 100, more fully described below.

With reference now to FIGS. 1, 2 and 4, the securing bracket 22rotatably attached to the lower end 24 of main shaft 12, comprises aback plate 50 and first and second side plates 52A and 52B to form agenerally U-shaped structure. Back plate 50 is provided with an aperture51 to allow bracket 22 to be attached by a bolt 53 to the lower end 24of main shaft 12. For this purpose, main shaft 12 is provided with anaperture 54 and a threaded nut 55 welded to the inside wall of tubing 16as can be seen in the section A-A of FIG. 2.

First and second side plates 52A and 52B are respectively provided withan aperture 56 and an aperture and threaded nut 58 adapted to accepttherethrough the wing bolt 60 shown in FIG. 5A. The length of first andsecond side plates 52A and 52B is such that a vertical stud, or ahorizontal element of a building frame can be retained between the sideplates 52A and 52B and back plate 50 and wing bolt 60.

Side plate 52A is further provided with a second aperture and threadednut 62 at an intermediate position along the length of side plate 52A,adapted to accept the shorter wing bolt 64 shown in FIG. 5B. Wing bolt64 may be driven through the aperture and threaded nut 62 to engage withthe side of a vertical stud or horizontal member of a building frame tofirmly secure the securing bracket 22 to the frame member. Preferably,wing bolts 60 and 64 are attached to bracket 22 by short lengths ofchain 65 and 66.

With reference to FIG. 8, a pair of scaffold assemblies 10 and 10A areshown attached to the side of a building frame 70. Scaffold assemblies10 and 10A are spaced apart to suit the length of two side by sidebuilder's planks 44.

The portion of building frame 70 shown in FIG. 8 includes verticaluprights or studs 72, a top plate 74 and an intermediate noggin orhorizontal frame member 76. The hook structures 20 and 20A are hookedover top plate 74, with the securing bracket 22 of scaffold assembly 10secured to one of the studs 72 while the securing bracket of scaffoldassembly 10A is rotated at 90 degrees and secured to horizontal framemember 76.

In the arrangement shown in FIG. 8, the braced hook-on arms 14 and 14Ahave been attached to the upper pair of brackets. At this higher level,in some jurisdictions at least, it may be a requirement that thescaffolding arrangement of scaffold assemblies 10, 10A and planks 44 beprovided with a safety railing.

FIG. 6 shows a safety railing system 100 for use with scaffoldingelements 10 and 10A. Safety railing 100 is comprised of stanchions 102and horizontal top rail 104 and horizontal intermediate rail 106. Eachof top rail 104 and 106 is made up of telescoping sections so that thelength of the railings between adjoining stanchions may be readilyadjusted.

Preferably, stanchions 102 and rails 104 and 106 are interconnected bysnap-locks 108. The vertical safety rail support elements 48 and 48A ofbraced hook-on arms 14 and 14A are adapted to accept as insertsstanchions 102 and 102A of safety railing 100.

For added security, safety railing 100 is provided with a number ofcross braces 110 connected at an outer end by a snap-lock fitting 112either to top rail 104 as shown in FIGS. 1, 6 and 7, or to stanchion102. Cross brace 110 is provided at an inner end with a lockingstructure 114 adapted for attachment to main shaft 12 by hooking intothe upper brackets 25, when attached to top rail 104, or to 25A whenattached to a stanchion 102.

Locking structure 114 is shown in more detail in FIG. 7 and is ofsimilar construction to the spring-loaded mechanism of hook-on arm 14previously described. As for that mechanism, the spring-loaded pin 120of locking structure 114 passes through a hole 31 provided in brackets25 and 25A when a cross brace 110 is connected to main shaft 12, thuspreventing inadvertent disengagement of the cross brace and endangeringthe integrity of the railing system.

It will be understood that the scaffold assemblies of the presentinvention may be used equally effectively on timber, steel or aluminiumframing members. As well, the components making up the scaffoldingelements and safety railing may be fabricated out of steel, aluminium ora combination of these materials, and that the specific design detailsmay be modified without departing from the principles of the invention.

SUMMARY

The hook-on scaffold 180 is an adjustable apparatus which can be used bycarpenters/builders who are installing truss roofs and also floorbearers on two story buildings. The scaffold is used in a set of atleast two. It does not require tools when setting up. The scaffold,which can accommodate two side-by-side builder's planks, gives workers abigger safety area to walk on. The work area width is enlarged from 95mm to 460 mm. When set at correct working height, safety harnesses arenot required. Provision is made for a detachable safety rail.

The components making up the hook-on scaffold are:

1. MAIN SHAFT WITH SIX HOOKING EYES. 2. HOOK PLATE. 3. HOOK ON ARM. 4.SAFETY BRACKET. 5. LOCKING WING BOLT. 6. SPRING-LOADED MECHANISM 7.SAFETY RAIL 8. SAFETY RAIL CROSS BRACE

1. Main Shaft with Four Hooking Eyes.

The Main Shaft (12) is preferably a square tubing 50 mm by 50 mm by 1.6mm and the average length is 1.3 metres. Hooking eyes (26) and (26A) arewelded to the main shaft (12) at the required safety height with a 6 mmgap from the main shaft (12). Hooking eyes (23) and (26) are differentto hooking eyes (23A) and (26A) in that they have a hole to enable aspring-loaded pin to lock the hook-on arm (14) to the main shaft (12).There is a nut (55) welded inside the bottom of the main shaft (12) towhich the safety bracket (22) is attached. Main Shaft (12) also hasfurther hooking eyes (25) and (25A) for attachment of a safety railcross brace (110).

2. Hook Plate.

The Hook Plate (20) is welded to the main shaft (12) which hangs overthe top plates of timber/metal frame. The hook plate (20) is 100 mm wideto suit 95 mm to 100 mm top plates. It may be reinforced with astrengthening rib (21)

3. Hook on Arm.

The hook on arm (14) is made from steel which consists of two bars, thefirst being a horizontal bar and the other bar is at an angle. It has anon adjustable hooking lug (34) and (36) at the end of the horizontalbar (28) and the end of the angle bar (30). Hooking lug (34) has a holein it to enable a spring-loaded pin (38) to lock the hook on arm (14) tothe main shaft (12). For extra strength braces (32) are welded betweenthe horizontal bar (28) and the angle bar (30). The hook on arm (14)hooks into the hooking eyes (26), on the main shaft (12), which are setat the appropriate working height conditions. At each end of the arm isa plank safety hook (40) & (42) to hold the two planks in place andbetween each plank there is a divider lug (46). On the outside of thehook on arm (14) a cylinder (48) is welded to hold the safety rail(100).

4. Safety Bracket.

The safety bracket (22) is bolted to the main shaft (12) and locksaround the stud of timber/metal. The safety bracket (22) is a ‘U’ shapedframe of flat steel. It is held in place around the stud by a wing bolt(60). The safety bracket (22) can be rotated 90 degrees to suit nogginson a frame. The safety bracket (22) consists of a back plate (50) whichcan be rotated and has a hole (51) to insert a bolt (53) to attach thesafety bracket (22) to the main shaft (12). Two side plates (52A) &(52B) are attached to the back plate (50). Side plate (52A) has two nutswelded to accommodate wing bolts (60) & (64) and safety chain (65) isalso welded to it. Side plate (52B) has a hole to accommodate wing bolt(60), and the safety chain (66) is also welded to it.

5. Locking Wing Bolt.

A wing bolt (60) is at the end of the safety bracket (22) and a lockingwing bolt (64), which bites into the stud, is half way along the safetybracket (22). The two wing bolts are on opposite sides of the safetybracket (22). Attached to each wing bolt (60) & (64) are safety chains(66) & (65). On each wing bolt (60) & (64) there is a spacer washer tocontrol penetration of the wing bolts.

6. Spring-Loaded Mechanism

The spring-loaded mechanism (33) is a safety feature that secures thehook-on arm (14) to the main shaft (12). The spring-loaded mechanism(33) consists of a U-shaped bracket (41), spring-loaded pin (38) andspring (43). Pin (38) extends through holes in bracket (41) and isprovided with a hole (47) for attachment of a split ring (45). Pin (38)is further provided with a washer (39) welded to the shaft of the pin.

7. Safety Rail.

The safety rail (100) consists of two horizontal rails (104) & (106)utilising telescopic aluminium tubing. There are two upright posts(102), each having two snap lock hooks (108), one hook being at the topof the post and the other at the centre of the post. The bottom end ofthe upright post (102) is inserted into the cylinder (48) welded to thehook-on arm (14). The Safety rail (100) is held in place by the snaplock hooks (108) to upright posts (102). A locking arm (110) locks thesafety rail (104) to the frame with a snap lock on one end and a hook(114) on the other end. The hook has a hole so it can be fixed to theshaft.

The above describes only some embodiments of the present invention andmodifications, obvious to those skilled in the art, can be made theretowithout departing from the scope and spirit of the present invention.

1. A scaffold assembly comprising at least one pair of hook-on scaffoldelements; said scaffold elements adapted for support of at least onebuilder's plank; each of said elements comprising a vertical main shaftprovided with a hook structure at an upper end of said main shaft and asecuring bracket at a lower end of said main shaft; each of said hook-onscaffold elements further comprising a braced hook-on arm; said hookstructure adapted for engagement with a horizontal top plate of abuilding frame, and said securing bracket adapted for engagement with avertical stud or a horizontal element of said building frame.
 2. Thescaffold assembly of claim 1 wherein said assembly further comprises asafety rail assembly for attachment to said pair of hook-on scaffoldelements.
 3. The scaffold assembly of claim 1 wherein said vertical mainshaft comprises a length of metal rectangular hollow section; said mainshaft provided at intervals along its length with hooking eyesprojecting from said main shaft in a first outward direction; saidhooking eyes adapted for engagement with said braced hook-on arm.
 4. Thescaffold assembly of claim 1 wherein said hook structure comprises ametal horizontal plate projecting from said upper end of said main shaftin a second inward direction; said hook structure further including ametal vertical plate depending from an outer end of said horizontalplate.
 5. The scaffold assembly of claim 4 wherein said metal horizontalplate is provided with a strengthening rib extending substantially thelength of said plate.
 6. The scaffold assembly of claim 4 wherein saidsecuring bracket comprises a generally U-shaped fabrication comprising aspaced apart pair of arms extending from a back plate in said secondinward direction; said arms adapted to accept between them a saidvertical stud or a horizontal element of said frame.
 7. The scaffoldassembly of claim 6 wherein said pair of arms are of a length so as toproject past an inner face of said vertical stud or horizontal element;outer ends of said arms provided with apertures adapted to accepttherethrough a securing element so as to secure said securing bracket tosaid vertical stud or said horizontal element.
 8. The scaffold assemblyof claim 7 wherein said securing element is a first wing bolt passingthrough a first of said apertures in a first of said arms and threadablyengaging with a threaded one of said apertures in a second of said arms.9. The scaffold assembly of claim 1 wherein one of said arms is providedwith a threaded aperture at a median position along said arm; saidthreaded aperture adapted to accept a second wing bolt; said second wingbolt adapted for engagement with said vertical stud or said horizontalmember so as to prevent any movement of said bracket relative saidvertical stud or said horizontal element.
 10. The scaffold assembly ofclaim 9 wherein each said first wing bolt and said second wing bolt aresecured to said bracket by a length of chain.
 11. The scaffold assemblyof claim 1 wherein said securing bracket is rotatably attached to saidmain shaft; attachment of said securing bracket arranged so as to allowsaid bracket to rotate 90 degrees between a first position forengagement with said vertical stud and a second position for engagementwith said horizontal element.
 12. The scaffold assembly of claim 3wherein said hooking eyes comprise U-shaped elements projectinghorizontally from said main shaft; arms of said U-shaped elementsattached to opposing sides of said main shaft, and wherein separationbetween an outer face of said main shaft and inside faces of cross barsof said U-shaped elements is adapted to accept hooking lugs of saidbraced hook-on arm.
 13. The scaffold assembly of claim 3 wherein saidmain shaft is provided with at least one pair of said hooking eyes. 14.The scaffold assembly of claim 3 wherein said main shaft is providedwith two pairs of said hooking eyes; said two pairs providing two levelsof attachment of said hook-on arm.
 15. The scaffold assembly of claim 13wherein one of each of said at least one pair of hooking eyes isprovided with an aperture through said cross bar of said U-shapedelement; said aperture adapted to receive a spring-loaded pin forsecuring one of said hooking lugs inserted in said hooking eye.
 16. Thescaffold assembly of claim 1 wherein said braced hook-on arm comprises ahorizontal support member, an angled bracing member and at least oneintermediate brace member extending between said horizontal supportingmember and said angled bracing member.
 17. The scaffold assembly ofclaim 16 wherein an inner end of each of said horizontal support memberand said angled bracing member is provided with one of said hookinglugs; each respective one of said hooking lugs adapted for insertioninto a corresponding one of said pair of hooking eyes.
 18. The scaffoldassembly of claim 16 wherein one of said hooking lugs for saidhorizontal support member is provided with an aperture adapted forpassage therethrough of said spring-loaded pin; said spring-loaded pinpassing through said aperture in a said hooking eye when said bracedhook-on arm is assembled to said main shaft.
 19. The scaffold assemblyof claim 16 wherein said horizontal support member is of lengthsufficient to support thereon two side-by-side said builder's planks.20. The scaffold assembly of claim 19 wherein an inner end and an outerend of said horizontal support member are provided with retaining planksafety hook elements; said safety hook elements adapted to retainrespective outer edges of said side-by-side builder's planks. 21-32.(canceled)